My husband's fell under our physical therapy benefit which was a straight dollar benefit, no co-pays each time.
Something to look into: Check to see if your policy as an out of pocket maximum or breakpoint. Co-pays usually don't apply to this, but if you're on a 90/10 plan, check to see if you're reached your maximum. Insurance companies frequently "forget" you've reached the maximum out of pocket and continue to pay out at the 90%.
Example: My plan has a $15,000 breakpoint - this means that our company only has to pay $15,000 per employee per year and over that the insurance company pays (we're self-funded). On the employee end, their out of pocket per year maximum is 10% of the breakpoint = $1,500. So, if you satisfy your deductible ($500 for our plan), you then pay 10% of all costs (except co-pays) up to $1,500. The plan then turns into a 100% paid plan. When you have surgery, you hit that in the first day!